Re: [exim] using MX always

On 8 Jan 2006, at 01:52, Jeff Lasman wrote:

> On Saturday 07 January 2006 04:17 pm, Giuliano Gavazzi wrote:
>> perhaps it's because it is too late, but I miss your point. The first
>> router is usually:
>>
>> dnslookup:
[...]
>> and this does exactly what, in my current understanding, you say.
>
> As far as I understand it, this router uses remote_smtp only for
> domains
> that are not listed as local_domains. The problem is that someone
> logs
> in to our configuration system and sets up a domain. They use their
> email address at that domain as their contact address.
>

ah, but this is a consistency nightmare! You should not allow them to
use a domain identical to the domain they set up with you, or, if
that domain already exists you should not add that domain to your
local domains until you have set up the dns for it (with MX pointing
to you).

> They never get our welcome email and we lose a customer, often
> having to
> refund a CC payment or accept a chargeback.
>
> If I comment out (or remove) the line beginning "domains" then
> it'll use
> remote_smtp for all email addresses, but cause too many mail-loop
> considerations.

bad idea indeed, but it can be improved..

> I don't think what we'd like is possible, but we can achieve similar
> effect by sending out welcome emails using a different server, which
> would get the old MX address from public DNS.

well, by definition the MX obtained from the DNS is not old...
however can be stale if the queried server has got it cached.

You can achieve something similar to what you say this way:

have two lists:

local_domains = your permanent local domains
customers_domains = your customers added domains

then in the dnslookup router instead of

domains = !+local_domains

something like (in pseudo exim acl code, because it's too late):

condition = {$domain not in local_domains} OR !{ MX($domain) =
this_host }

and the local delivery router uses

domains = local_domains : customers_domains

You must not add the DNS for the new customer domain until after you
have sent the welcome message and the domain has been transferred.

I am not sure what !{ MX($domain) = this_host } evaluates to if there
is no MX record (it can happen of course). There might be an option
in the dnslookup to make it true. Otherwise just add the A lookup too.

Giuliano